1. Field of the Invention
The invention relates to manufacturing a thin film transistor used as a switching device of a liquid crystal display device, and more particularly, to a method for reducing the number of masks used when manufacturing a thin film transistor.
2. Description of the Conventional Art
Generally, a liquid crystal display (LCD) device displays desired information on a screen by controlling the alignment direction of a liquid crystal aligned by an electric field applied between a pixel electrode formed on a TFT (thin film transistor) array substrate and a common electrode on a color filter. Here, the thin film transistor is mainly used as a switching device for applying a voltage to the pixel electrode existing on the TFT array substrate.
The number of masks used for manufacturing the LCD device directly affects the number of process steps. Decreasing the number of process steps increases productivity and yield. Accordingly, one tries to reduce the number of masks used in manufacturing the thin film transistor.
The related art methods for manufacturing TFTs utilize a 5-mask or 4-mask process.
A manufacturing process of a TFT of an LCD device using a related art 5-mask will be explained with reference to FIGS. 1A to 1E.
FIG. 1A shows a gate electrode material being formed on a substrate 1. The gate electrode material is a metal material, and is formed by sputtering.
The metal layer for forming the gate line also serves as a storage line for maintaining the voltage at a TFT for a predetermined time, and it also serves as a gate pattern of a gate pad portion.
After forming the gate metal layer, photoresist (not shown) is deposited on the metal layer, and a photolithography process is performed using a first mask (not shown), thereby selectively forming a gate line, a storage region line, and a gate pattern 2 in the gate pad region on the substrate 1.
FIG. 1B shows a gate insulating layer 3, an active layer of semiconductor, and a high-concentration impurity layer that are sequentially formed on the resulting material. Then, photolithography is performed using a second mask (not shown) to thus selectively etch so that an active region 4 forms in the channel region. Here, the active region 4 is formed by stacking an amorphous silicon (a-Si) and an ohmic contact layer, and a high-concentration of impurity is doped into the semiconductor layer.
The gate insulating layer and the active layer are generally deposited using a plasma enhanced chemical vapor deposition (PECVD) method.
FIG. 1C shows source/drain electrode material that are formed on the resulting material. Then, photolithography is performed using a third mask (not shown) to thus selectively etch so that the source/drain material can be separated from each other at both sides of the active region 4 at the channel region. Also, the source/drain material can be applied as one electrode 7 of a capacitor on the gate insulating layer 3 at the storage region, and the source/drain material can also be applied as a data electrode 8 on the gate insulating layer 3 of a data pad portion.
FIG. 1D shows a passivation layer 9 being formed on the resulting material. Then, a contact hole is formed using a fourth mask (not shown) so that the drain region 6 of the channel region, the electrode 7 of the storage region, the gate pattern 2 of the gate pad portion, and the data electrode 8 of the data pad portion can be exposed.
FIG. 1E shows an electrode material being formed on the resulting material. Then, photolithography performed by a fifth mask (not shown) forms a pixel electrode 10 connecting the drain region 6 of the channel region and the electrode 7 of the storage region. At this time, a gate line and a data line are simultaneously formed on the gate pad portion and the data pad portion.
The aforementioned method for manufacturing an LCD device by using a 5-mask process limits the possibilities to reduce manufacturing cost and to simplify processes due to the performance of multiple photolithographic steps.
In order to solve this problem, a related art LCD device manufacturing method using a 4-mask process was proposed.
A manufacturing process for an LCD device using a 4-mask process will be explained with reference to FIGS. 2A to 2G.
FIG. 2A shows a gate electrode material that is formed on a glass substrate 21. Then, a photolithography process using a first mask (not shown) is performed to thereby selectively form a gate line, a line of the storage region, and an electrode pattern 22 on the substrate 21.
FIG. 2B shows a gate insulating layer 23, an active layer 24, and a conductive layer 25 of a metal that are sequentially formed on the resulting material. Here, the active layer 24 is a stacked layer of a semiconductor layer and a high-concentration impurity layer.
In FIG. 2C, a photoresist layer (not shown) is formed on the conductive layer 25. Then, a photolithographic step using a second mask (not shown) patterns the photoresist layer 40 remaining on the channel region, the storage region, and a data pad portion. A stepped photoresist pattern forms on the conductive layer 25 at the channel region by applying a diffraction exposure to the photoresist layer 40. A source/drain electrode and a channel are formed by using the stepped photoresist pattern as a mask.
FIG. 2D shows that the conductive layer and the active layer of regions where the photoresist pattern is not present are etched and removed by using the photoresist layer 40 pattern as a mask.
FIG. 2E shows the diffraction-exposed photoresist pattern being partially removed by an ashing process, and the conductive layer above the channel region is exposed.
Thereafter, the photoresist layer 40 pattern is selectively removed to thus etch the exposed electrode layer 25 above the channel region. Next, the active layer 24 is etched to a predetermined thickness to form source/drain electrodes 26 and 27 separated from each other at both sides on the active layer 24. Then, as shown in FIG. 2F, the remaining photoresist layer 40 pattern is removed.
FIG. 2G shows a passivation layer 28 that is formed on the entire resulting material. Then, a photolithography step is performed using a third mask (not shown) to selectively etch so that the drain electrode 27 of the channel region, the electrode layer 25 of the storage region, the gate pattern 22 of the gate pad portion, and the electrode layer 25 of the data pad portion can be exposed.
FIG. 2H shows an electrode material that is formed on the resulting material. Then, a photolithography process is performed using a fourth mask (not shown) to selectively etch so that a pixel electrode 29 connecting the drain region 27 of the channel region and the electrode layer 25 of the storage region can be formed. Also, a line 30 connected to the gate pattern 22 of the gate pad portion and a line 31 connected to the electrode layer 25 of the data pad portion can be simultaneously formed during this step.
In this related art manufacturing method of an LCD device using the 4-mask step photolithographic process, the manufacturing cost can be reduced and processes can be simplified compared to the manufacturing method of an LCD device using a 5-mask step photolithographic process.
That is, minimizing the number of masks contributes to reducing the manufacturing cost and to simplifying the overall process.
However, efforts to reduce the number of masks used in manufacturing LCD devices are being continued. The invention is therefore directed at developing an LCD manufacturing method in which the number of masks is minimized when compared to the related art.